In the field of ac discharge laser, conventionally laser apparatuses using a silent discharge (ozonizer discharge) under ac voltages having frequencies of 100 KHz and below are provided.
The present inventor has created a high frequency power unit for generating a gas laser, in which a power supply per unit volume has been increased by applying ac voltages having higher frequencies of several hundreds KHz.about.several tens MHz, and further, has reduced the size of the unit by using solid state components.
FIG. 1 shows a conventional construction of a high frequency power unit for generating a gas laser 1', which is used in the prior art apparatus for generating a laser. The high frequency power unit for generating a gas laser 1' comprises a rectifying and smoothing circuit 11 and a high frequency inverter 13. The rectifying and smoothing circuit 11 rectifies and smoothes an ac current to dc current. FIG. 2 shows the construction of an example of the rectifying and smoothing circuit 11. The high frequency inverter 13 transforms a dc current to a high frequency current. FIG. 3 shows the construction of an example of the high frequency invertor 13. The matching circuit 2 in FIG. 1 is provided for matching the output impedance at the output terminals of the high frequency invertor 13 and the input impedance at the input terminals of a laser tube 3. The matching circuit 2 is realized, for example, by a II-type filter. The wave shape of the high frequency output of the matching circuit 2 is similar to the shape of a sine wave, and the high frequency output is applied between the two electrodes of the laser tube 3.
No problem arises when the high frequency power unit for generating a gas laser 1' shown in FIG. 1 is used in the continuous output mode (CW mode), but, a high speed control of the high frequency power unit for generating a gas laser 1' is impossible.
An intermittent laser output, having a frequency of a maximum of 5 KHz, is often required in the field of laser beam machining. For example, when cutting or machining copper or aluminium, it is necessary to apply a pulsed (intermittent) laser output having a high intensity to instantaneously melt the material, and thereby improve the absorption rate of the laser beam. But it is impossible to control (pulsed drive) the laser output at a frequency as high as 5 KHz.
As shown in FIG. 2, a commercial ac current is rectified and smoothed in the smoothing circuit which consists of a coil and a condenser for smoothing ripples in the current rectified from the ac current having the commercial power frequency (50 Hz), in the rectifying and smoothing circuit 11 in FIG. 1. Accordingly, it is impossible to control the output at high speed in the power supply apparatus shown in FIG. 1.
To solve the above problem, a high frequency power unit for generating a laser 1" as shown in FIG. 4, in which a series regulator 14 is provided between the rectifying and smoothing circuit 11 and the high frequency invertor 13, is currently used. Two examples of the construction of this series regulator are shown in FIGS. 5A and 5B.
It is possible to control (pulsed drive) the laser output at a frequency such as 5 KHz, for example, by applying the pulsed input to the base terminal of the transistor to output a constant voltage in the series regulator as shown in FIGS. 5A or 5B.
Nevertheless, because a load and a transistor for voltage control are generally connected in series in a series regulator, the power consumption in the transistor is high, and therefore, the efficiency of utilizing electric power is low, and further, a heat sink is necessary to absorb heat generated in the transistor, which enlarges the size of the power unit.